My eldest is 23 and earns good money, but all over the world, so he gets a little money, and if he is home, a small under the tree gift.
I felt that 18 was the cut off, but I did not see much of him growing up as his parents and grandparents did not celebrate Christmas and he was separated from my son. Also the other 3 are much younger, but last year 2nd dgs asked for money towards a much bigger item - he will get money this year.
DH is somewhat mean about money, so they have got used to smaller gifts than other grandparents give (mind you they offer holidays, bikes, games consoles etc)